The present invention relates generally to air distribution systems used to control the ambient temperature in an enclosed area. More specifically, the present invention relates to pneumatic apparatus for use in such systems wherein it is necessary or desirable to provide, during certain periods of operation, maximum air flow into the areas serviced by such systems independently of the ambient temperature therein.
Systems for automatically controlling the environmental temperature in habitable, enclosed areas generally employ a source of pressurized air which supplies air through ducts to the various rooms of the enclosure. In each room one or more terminal ports are utilized which typically employ ceiling mounted diffusers to distribute the conditioned air evenly throughout the room. In addition, such systems utilize a temperature sensing device and a controller which meters the volume of air discharged in response to changes in ambient temperature.
When an air distribution system such as that generally described above is used to control the ambient temperature in an enclosed area by the discharge of cool or chilled air thereto, the temperature sensing device and controller are typically arranged so that, as the temperature in the room increases, the controller allows greater volumes of chilled air to be discharged. In view of the fact that sometimes the area serviced by the air distribution system is at a very low ambient temperature when the system is started, as for example in the morning, prior art systems have provided for a warm up cycle which allows the discharge at the start-up period of warm or heated air. It is, of course, desirable to have as short a warm up cycle as possible and, thus, it is important that the volume controllers be adjustable to provide maximum air flow during these warm up periods. Unfortunately, the environmental or ambient temperature is very low at the start of the warm up period. The primary pneumatic circuitry utilized to control air flow during normal cooling periods will, therefore, operate to close down and provide minimum air flows to the enclosed areas during these warm up periods. Accordingly, in cool air distribution systems which require a warm up capability it is necessary to provide means for overriding or nullifying the pneumatic circuitry ordinarily used in the operation of the system such that maximum air flow will be provided to the enclosed area during the warm up cycle.
Typical prior art systems which provide such override capabilities are those disclosed in U.S. Pat. Nos. 3,743,180 and 3,806,027. These prior art systems, however, suffer from several disadvantages including the need for additional complex mechanical and pneumatic components which renders the air distribution system more expensive to manufacture, assemble and install.
Accordingly, the present invention is directed to an apparatus for use in an air distribution system, the apparatus having the capability of overriding the primary pneumatic circuitry which controls the discharge of cooling air into the enclosed area during the normal cooling cycle. The present invention finds a particularly advantageous application in an air distribution system which includes means for converting a variable pressure air supply to a substantially constant pressure air flow which constant pressure air flow is then utilized in generating a pneumatic signal indicative of ambient temperature. In such a system the substantially constant pressure air flow is transmitted to a pneumatic thermostat which generates the pneumatic signal in responses to changes in the ambient temperature. In accordance with the present invention means are provided for reducing the pressure of the substantially constant pressure air flow to a value sufficiently low to effectively nullify the function of the pneumatic thermostat, thereby allowing the volume controller to provide maximum air flow during the warm up cycle. In order to render the override apparatus independent of any external energy source, the override mechanism of the present invention is activated by the introduction into the air distribution system of heated air which is, of course, necessary for the warm up cycle.